1. Field of the Invention
The present invention relates to a highly accurate judging system for detecting a failure of a machine to indicate a possible fault.
2. Description of the Prior Art
FIG. 1 shows one embodiment of the conventional judging system for detecting a failure.
Referring to FIG. 1, the conventional judging system for detecting the bearing failure will be described. In the block diagram of FIG. 1, the reference numeral (1) designates a sensor-amplifier unit which detects sampling signals representative of the bearing vibration of a machine (not shown) and amplifies the detected signals as desired. An effective value detection unit (2) and a peak value detection unit (3) which detect respectively the effective values and the peak values of the output signals from the sensor-amplifier (1) are connected to the output of the sensor-amplifier (1). Comparator units (4), (5) are respectively connected to the outputs of the effective value detection unit (2) and the peak value detection unit (3) so as to compare the outputs of the effective value and the peak value with the set values. A discrimination unit is connected to the outputs of the comparator units (4), (5) so as to judge whether it is in the normal state or the abnormal state depending upon the results of the comparisons in the comparison units (4), (5). The discrimination unit (6) output is fed to the display unit (7).
When the judging system is used for detecting whether or not bearing failure has occurred by detecting either the abnormal state or the normal state, various problems are found.
In a first instance, there are the problems with the values obtained by the effective value detection unit (1) and the peak value detection unit (5) because of a possibility ot an error in the peak value depending upon the frequency component of the waveform and secondly there arises the problem of an erroneous operation.
Usually this judging unit is used in a practical driving of the machine. In that case, the shock waveform caused by the starting or the stopping or the external disturbance in a maintenance operation may be erroneously judged to cause an abnormal state of the bearing as a bearing failure.
The erroneous judgement will be further described, especially the vibration phenomenon in the bearing failure will be described.
When the kind of the bearing is a rolling bearing, the possible abnormal phenomena include a seizure caused by a lubricant shortage, an impurity contamination and a failure caused by various parts of the bearing. In every case, the effective value or the peak value of the vibration is increased. The increased value will not be lowered except by treating the bearing in a certain manner.
A ratio of the increased value at the initial abnormal state which is caused by a lubricant etc., to the original value is only 3 to 5 times. The ratio is not substantially different from that of the external noise signal caused by the starting, the stopping and the installation. Therefore, it is premature to judge the bearing failure only by the increase of the effective value or the peak value.